1. Field of the Invention
The invention is directed to an improved high-pressure pump for a fuel injection system of an internal combustion engine.
2. Description of the Prior Art
One high-pressure pump known from German Patent Disclosure DE 198 44 326 A1 has a rotationally driven drive shaft and at least one pump element, with a pump piston driven at least indirectly in a reciprocating motion by the drive shaft. The pump piston is guided in a cylinder bore and, with its end remote from the drive shaft, defines a pump work chamber. The pump piston is braced at least indirectly on the drive shaft. The drive shaft has a portion which is eccentric to its pivot axis, supported on which is a ring on which the pump piston is braced directly with its piston base or via a tappet. The ring does not rotate with the drive shaft, but in operation of the high-pressure pump, a sliding motion occurs between the piston base or tappet and the ring. Lubrication of the contact region between the piston base or tappet and the ring is effected only by the fuel present in the interior of the high-pressure pump, so that under some circumstances severe wear to the pump piston and/or the tappet and/or the ring occurs, which can finally lead to failure of the high-pressure pump. The tappet may be guided displaceably in a bore in the housing of the high-pressure pump, in order to be braced against transverse forces so that they do not act on the pump piston. Lubrication between the tappet and the bore is likewise accomplished only by the fuel located in the interior of the high-pressure pump, and hence major wear to the tappet and/or the housing can also occur.
From German Patent Disclosure DE 199 07 311 A, a high-pressure pump for a fuel injection system is also known in which the drive shaft has at least one cam, on which the pump piston is braced via a tappet and a roller rotatably supported in the tappet. The bearing of the roller is again lubricated only by the fuel present in the interior of the high-pressure pump, so that wear can occur here as well.